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Investments - Additional Information (Detail) - USD ($) | 3 Months Ended | 6 Months Ended | 9 Months Ended |
--- | --- | --- | --- | ---
Sep. 30, 2025 | Jun. 30, 2025 | Sep. 30, 2025 | Sep. 30, 2024 | Dec. 31, 2024
Investments, Debt and Equity Securities [Abstract] |  |  |  |  |
Principal amount of bonds and certificates of deposit | $ 788,000,000 |  | $ 788,000,000 |  |
Securities exceeding 10% of Shareholders' Equity | 0 |  | 0 | $ 0 | $ 0
Non-income producing securities | 0 |  | 0 |  |
Debt securities, available-for-sale, allowance for credit loss, not previously recorded |  |  | 0 | 0 |
Debt securities, available-for-sale, allowance for credit loss | $ 0 |  | 0 | 0 | $ 0
Debt securities, available-for-sale, allowance for credit loss, write-off |  | $ 0 | $ 0 | $ 0 |
Percent change in investment income | 25.00% |  | 28.00% |  |

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